Synthesis and Spectroscopic Investigation of Sensitized Near-Infrared Emission of Yb3+ Complexes

Abstract

Lanthanide complexes possess unique photophysical properties such as sharp emission lines, large Stokes shifts, long luminescence lifetimes, and excellent photostability, making them ideal for applications in bioimaging, light-emitting devices, and telecommunications. Their ability to emit in the near-infrared (NIR) region (700–1700 nm) offers key advantages for medical and technological uses, including deep tissue penetration, minimal autofluorescence, reduced light scattering, high signal-to-noise ratios, and low toxicity. This study reports the synthesis and photophysical characterization of Yb3+ complexes across two similar projects. First, a porphyrin-based complex, [Yb(DPP)(PH)(OAc)(MeOH)], incorporating a phenylhexanone (PH) substituent, was synthesized and characterized using ¹H NMR, MS, FTIR, and UV-Vis spectroscopy. The complex exhibited visible absorption at 411 nm (Soret band) and weaker Q bands at 500 and 542 nm. Weak porphyrin fluorescence was observed at 635 and 700 nm, alongside near-infrared (NIR) emissions at 975 and 1006 nm corresponding to Yb3+ 2F5/2 → 2F7/2 transitions. The characterization data reveal that the complex possesses a highly asymmetrical coordination environment, which facilitates enhanced radiative transitions and indicates efficient energy transfer from the coordinated ligands to the Yb3+ ion. In a second study, BODIPY-functionalized ligands (L1–L4) were spectroscopically titrated with [Yb(DPP)(OAc)(MeOH)2] and [Yb(Hfac)3(H2O)2] to probe energy transfer and NIR emission behavior. Ligands L1 (Phen-BDP) and L2 (BiPy-BDP) sensitized Yb3+ emission efficiently in both complexes via the heavy atom effect, while L3 (PA-BDP) and L4 (UR-BDP) showed selective energy transfer only in [Yb-DPP-OAc-L], mediated by a stepwise FRET process. Based on these findings, four BODIPY-Yb3+ complexes were synthesized, each showing visible absorption (503–506 nm) and characteristic NIR emission around 980 nm, with peak splitting due to crystal field interactions.

Date of Award	2025
Original language	American English
Awarding Institution	Eastern Illinois University
Supervisor	Hongshan He (Supervisor)